1. Field of Invention
The invention relates to a novel memory cell structure and process to fabricate chalcogenide phase change memory. More particularly, it produces a small cross-sectional area of a chalcogenide-electrode contact part of the phase change memory, which affects the current/power requirement of the chalcogenide memory.
2. Background
Chalcogenides have been utilized in the formation of memory cells for integrated circuit memory devices. Representative prior art patents in this field include Reinberg, U.S. Pat. No. 5,789,758; Harshfield, U.S. Pat. No. 6,077,729; Wolstenholme, et al., U.S. Pat. No. 6,153,890, Ovshinsky, U.S. Reissue Pat. No. RE37,259 (Reissue of U.S. Pat. No. 5,687,112), and many others.
Chalcogenides used for integrated circuit memory devices are materials characterized by more than one solid-state phase, and which can be switched between such phases using the application of heat caused for example by electrical current or optical pulses. Memory cells which include a chalcogenide element are arranged in an array which can be addressed using conventional word lines/bit line addressing schemes common in integrated circuit memories. The state of the memory cell is determined by the bulk resistance of the chalcogenide element. Because the different solid-state phases of the chalcogenide have different resistivity, the bulk resistance of the chalcogenide element indicates the amount of the chalcogenide element in a selected phase state.
The problem of applying current at sufficient current densities to cause the phase change in the chalcogenide element is reflected in the design of the memory cells. Typically, relatively complex structures are utilized to form small pores in the current path that is coupled to the chalcogenide element. Current is concentrated through the small pores to induce a locally high current density in the chalcogenide element.
The complex structures utilized to form the pores, and other aspects of chalcogenide based memory cells, have required relatively large cell sizes to implement. Furthermore, complex structures can affect the reliability of the memory devices. Large cell sizes limit the density of the memory device, and increase its cost. Likewise, reliability in manufacturing is critical to successful commercial application of memory devices. High-density, self aligned memory cells have been manufactured for other types of storage technologies, such as the vertically stacked, non-volatile memory described in Johnson et al., U.S. Pat. No. 6,185,122.
One approach to producing higher density cells is proposed by Wicker, U.S. Pat. No. 6,597,009, entitled “Reduced Contact Area of Sidewall Conductor”. In Wicker's design, a trench 250 is the size of or narrower than a phase change material plug 290. The phase change material plug is aligned over one of two sidewall conductors 260 that are electrically coupled. Plugs of phase change material 290 are discontinuous and separated by an insulator.
Accordingly, it is desirable to provide phase change memory cell structures and devices with smaller sizes and power requirements. Furthermore, it is desirable to provide methods for manufacturing such devices, which are efficient and result in reliable structures.